JP-H10-110758A, JP-2001-165207A and JP-H10-103391A disclose duo-servo parking brakes in each of which, when a cable is pulled, a pair of brake shoes are moved through a brake lever and a strut so as to be pressed against a rotary drum whereby the parking brake is brought into effect. JP-2001-82517A discloses an electrically-operated parking brake system having a duo-servo drum brake. This parking brake system includes a pressing device having (a) an electric motor, (b) a pair of sliding members, (c) a motion converting mechanism disposed between the electric motor and the sliding members, and configured to convert a rotary motion which is to be given from the electric motor, into linear motions which are directed in respective opposite directions and which are to be given to the respective sliding members, and (d) a motor controlling portion configured to activate the electric motor in response to a command requesting operation of the brake, so as to move the sliding members in respective opposite directions and accordingly apply pressing forces to respective brake shoes, for thereby causing the brake to come into effect. JP-2006-336868A also discloses an electrically-operated parking brake system having a duo-servo drum brake. This parking brake system includes a pressing device having (a) an electric motor, (b) an eccentric cam, (c) a pair of sliding members engaged with an outer circumferential surface of the eccentric cam, and (d) a motor controlling portion configured to activate the electric motor in response to a command requesting operation of the brake, so as to rotate the eccentric cam, move the sliding members in respective opposite directions and accordingly apply pressing forces to respective brake shoes, for thereby causing the brake to come into effect.
JP-H10-110758A discloses a parking drum brake including (a) a non-rotary body, (b) a rotary drum rotatable together with a vehicle wheel, and having an inner circumferential surface that serves as a friction surface, (c) a pair of brake shoes disposed on an inner peripheral side of said rotary drum, and having respective outer circumferential surfaces on each of which a friction material member is disposed, (d) an anchor fixed to the non-rotary body and disposed between anchor-side end portions of the respective brake shoes, (e) a brake lever pivotably connected at its anchor-side end portion to one of the brake shoes through a pin, (f) a cable configured to pull another end portion of the brake lever (which portion is remote from the anchor), (g) an intermediate lever pivotably connected at its intermediate portion to the other of the brake shoes, (h) a strut disposed between the anchor-side end portions of the brake lever and the intermediate lever, and (i) an adjuster disposed between another end portion of the above-described one of the brake shoes (which portion is remote from the anchor) and end portions of the above-described other of the brake shoes and the intermediate lever (which portions are remote from the anchor), wherein a distance between a pivot center of the intermediate lever and the strut is larger than a distance between the pivot center of the intermediate lever and the adjuster.
In this parking drum brake disclosed in JP-H10-110758A, when the cable is pulled, the brake lever is pivoted about the pin whereby the intermediate lever is pivoted through the strut. The pivot motion of the intermediate lever is transmitted to the above-described one of the brake shoes via the adjuster, whereby the one of the brake shoes is pressed against the rotary drum. Meanwhile, the above-described other of the brake shoes is pressed against the rotary drum by a force applied to the intermediate lever via the strut. In this instance, as a result of the pivot motion of the intermediate lever, a gap is formed between the adjuster and the other of the brake shoes. In this state in which the parking brake is being in effect, upon application of a torque causing the one of the brake shoes to be separated from the anchor, the one of the brake shoes and the brake lever are moved in a circumferential direction that reduces the above-described gap, whereby the intermediate lever is pivoted through the adjuster in an opposite direction (that is opposite to a direction in which the intermediate lever is pivoted when the cable is pulled). As a result of the pivot motion of the intermediate lever in the opposite direction, the brake lever is returned through the strut. Since the distance between the pivot center of the intermediate lever and the strut is larger than the distance between the pivot center of the intermediate lever and the adjuster, the strut causes the brake lever to be moved in an opposite direction opposite to a direction in which the brake lever is forced due to the applied torque. Consequently, a path of the cable engaged with the brake lever is increased whereby the cable is restrained from being slackened. Upon application of a torque causing the other of the brake shoes to be separated from the anchor, the other of the brake shoes is moved in a circumferential direction and the intermediate lever is pivoted, whereby the one of the brake shoes and the brake lever are moved through the adjuster in a direction toward the anchor. Consequently, the cable is avoided from being slackened.
JP-H10-103391A discloses a parking drum brake including (a) a non-rotary body, (b) a rotary drum rotatable together with a vehicle wheel, and having an inner circumferential surface that serves as a friction surface, (c) a pair of brake shoes disposed on an inner peripheral side of said rotary drum, and having respective outer circumferential surfaces on each of which a friction material member is disposed, (d) an anchor fixed to the non-rotary body and disposed between anchor-side end portions of the respective brake shoes, (e) a brake lever pivotably connected at its anchor-side end portion to one of the brake shoes through a pin, (f) a cable configured to pull another end portion of the brake lever (which portion is remote from the anchor), and (j) a strut disposed between the anchor-side end portion of the brake lever and an anchor-side end portion of the other of the brake shoes, wherein a first connection point P1 at which the strut and the brake lever are connected to each other lies on a line connecting a center O of the drum brake and a second connection point P2 at which the brake lever and the above-described one of the brake shoes are connected to each other, or lies on an anchor-side one of opposite sides of the above-described line, which one is close to the above-described other of the brake shoes.
In this parking drum brake disclosed in JP-H10-103391A, when the cable is pulled, the connection point P2 is moved along an arc about the center O, whereby the connection point P1 is moved in a radially outward direction, and the above-described other of the brake shoes is forced toward the anchor. Thus, when the pair of brake shoes are pressed against the drum, the above-described one of the brake shoes is separated from the anchor while the other of the brake shoes is not separated from the anchor. In this state in which the parking brake is being in effect, even upon application of a torque causing the one of the brake shoes to be separated from the anchor, it is possible to avoid reduction of a braking force, since the other of the brake shoes is held in contact with the anchor. Upon application of a torque causing the other of the brake shoes to be separated from the anchor, the one of the brake shoes is moved in a circumferential direction so as to be brought into contact with the anchor. In this instance, a path of the cable is increased whereby the cable is avoided from being slackened.
Further, in this parking drum brake disclosed in JP-H10-103391A, a return spring disposed between the anchor and the above-described other of the brake shoes is arranged to generate an elastic force larger than an elastic force generated by a return spring disposed between the anchor and the above-described one of the brake shoes. Owing to this arrangement, the other of the brake shoes can be made difficult to be separated from the anchor when the brake shoes are pressed against the drum.
JP-2001-165207A discloses a parking drum brake including (a) a non-rotary body, (b) a rotary drum rotatable together with a vehicle wheel, and having an inner circumferential surface that serves as a friction surface, (c) a pair of brake shoes disposed on an inner peripheral side of said rotary drum, and having respective outer circumferential surfaces on each of which a friction material member is disposed, (d) an anchor fixed to the non-rotary body and disposed between anchor-side end portions of the respective brake shoes, (m) a pair of intermediate levers each of which is pivotably connected at its intermediate portion to a corresponding one of the brake shoes, (n) a brake lever pivotably connected to an anchor-side end portion of one of the intermediate levers so as to be pivotable about a pin, (o) a cable for applying a tensile force to an end portion of the brake lever (which portion is remote from the anchor), (p) an adjuster disposed between end portions of the respective brake shoes (which portions are remote from the anchor) and between end portions of the respective intermediate levers (which portions are remote from the anchor), (q) a strut disposed between the other of the intermediate levers and each of the one of the intermediate levers and the brake lever, (r) a first return spring disposed between anchor-side end portions of the respective brake shoes, and (s) a second return spring disposed between adjuster-side end portions of the respective brake shoes, wherein a moment (F1×L1) dependent on an elastic force F1 of the first return spring and a distance L1 between a pivot center of each intermediate lever and the first return spring is larger than a moment (F2×L2) dependent on an elastic force F2 of the second return spring and a distance L2 between the pivot center of each intermediate lever and the second return spring.
In this parking drum brake disclosed in JP-2001-165207A, when the tensile force is applied to the cable, the pair of intermediate levers are pivoted about the adjuster so as to be spread or moved away from each other, whereby the pair of brake shoes are pressed against the drum. In this instance, since the moment dependent on the elastic force of the first return spring is larger than the moment dependent on the elastic force of the second return spring, the brake shoes are brought into contact at their anchor-side end portions with the anchor, while being separated at their adjuster-side end portions from the adjuster. In this state in which the parking drum brake is being in effect, upon application of a torque causing one of the brake shoes (to which the above-described other of the intermediate levers is connected) to be separated from the anchor, this one of the brake shoes is moved in a circumferential direction so as to be brought into contact with the adjuster, whereby the above-described one of the intermediate levers is pivoted, and the brake lever is pivoted about the strut serving as a fulcrum so as to be moved in a radially outward direction. Further, the brake lever is moved in the radially outward direction also when the one of the intermediate lever is forced in a circumferential direction by the adjuster. The movement of the brake lever in the radially outward direction leads to increase of a path of the cable, thereby preventing the cable from being slackened. Upon application of a torque causing the other of the brake shoes (to which the above-described one of the intermediate levers is connected) to be separated from the anchor, the other of the brake shoes is moved in a circumferential direction so as to be brought into contact with the adjuster, whereby the other of the intermediate levers is pivoted, and the one of the intermediate levers and the brake lever are pivoted via the strut so as to be moved in a radially outward direction. Further, the brake lever is moved in the radially outward direction by movement of the other of the brakes shoes in a circumferential direction which leads to pivot motion of the one of the intermediate lever. The movement of the brake lever in the radially outward direction leads to increase of a path of the cable, thereby preventing the cable from being slackened.